The present invention relates to a method of fixing a knife adjusting bolt provided at the bottom of a veneer peeling knife of a veneer lathe and used for adjusting the height of a ground cutting edge of the knife with the aid of a knife setting gauge. More specifically, the invention relates to the above knife adjusting bolt fixing method which expedites the knife setting procedure and also prevents the adjusted bolt from becoming loose and the height of the knife cutting edge from being brought out of adjustment during veneer peeling operation. The present invention also relates to a veneer peeling knife itself.
For the sake of aiding in understanding of the underlying problems of the invention, reference is made to FIGS. 12, 13 and 14. FIG. 12 shows a conventional veneer peeling knife 10 mounted in a knife carriage 13 of a veneer lathe. The knife 10 has a plurality of adjusting bolts 12 (only one bolt being shown in the drawing) inserted into respective threaded holes formed in the bottom of and along the longitudinal direction of the knife. For adjustment of the knife 10, each adjusting bolt 12 is screwed into the threaded hole and turned so that the knife is set with its cutting edge positioned at a predetermined elevation or height. For fixing the adjusting bolt 10 after the knife cutting edge has been set at the desired height, a lock nut 12a has been used which is provided on the bolt 12 and tightened into pressing abutment with the knife bottom surface. As is well known in the art, such adjustment of the knife 10 is usually performed on a knife setting gauge as indicated by reference numeral 1 in FIG. 1.
According to this conventional method, when the knife 10 is just adjusted for the desired cutting edge height with use of the knife adjusting bolt 12, the external thread of the adjusting bolt is engaged with the internal thread of the bolt receiving hole 14 such that the load of the knife 10 due to its weight is received by contact between the lower side flank (or slope) 10a of the internal thread of the hole 14 and the advancing side flank 12b of the external thread of the adjusting bolt 12, as illustrated in FIG. 13. When the lock nut 12a is then turned until it contacts the knife bottom surface and further turned, the lock nut pushes the knife 10 upward, displacing the lower side flank 10a of the internal thread of the hole 14 clear of the advancing side flank 12b of the adjusting bolt thread. When the lock nut 12a is further turned until the upper side flank 10b of the internal thread of the hole 14 is tightly pressed against the retracting side flank 12c of the external thread of the adjusting bolt 12 as shown in FIG. 14, the knife load is then received by contact engagement between the advancing side flank 12b of the external thread of the adjusting bolt 12 and the retracting side flank 12d of the internal thread of the lock nut 12a and also contact between the lock nut top surface and the knife bottom surface. It is noted that for the sake of illustration the threads of knife adjusting bolt 12, adjusting bolt receiving hole 14 and lock nut 12a are shown in FIGS. 13 and 14 with exaggerated lost motion or backlash between the engaged threads.
Apparently, tightening the lock nut 12a according to the above-described conventional method brings the height of the knife cutting edge out of adjustment by the amount corresponding to the backlash between the external thread of the adjusting bolt 12 and the internal thread of the hole 14. To correct the adjustment, the lock nut 12a is loosened and an adjustment is made again by turning the adjusting bolt 12. It has been a usual practice to repeat this procedure until the correct height of the knife cutting edge is obtained. Apparently, this does not only call for a technique of skilled maintenance personnel, but also takes a remarkable length of time.
During veneer peeling operation of the lathe, the veneer knife is subjected to a load acting in downward direction due not only to the knife weight but also to veneer peeling action, and a part of this load is applied to the retracting side flank 12d of the lock nut 12a which has a smaller number of threads, as counted in axial cross-sectional view as seen in FIG. 14, than the adjusting bolt 12 does. Therefore, the lock nut 12a tends to become loose or deformed under the influence of the load, with the result that the knife cutting edge is lowered from the adjusted height during veneer peeling operation. An increased number of adjusting bolts 12 may be used so as to reduce the magnitude of the load applied to each lock nut 12a, although this will only make the knife adjusting procedure more troublesome and time-consuming.